Tightening belt - Call me Stupid!

I have a 1987 260E. The serpentine belt looks to be in great shape, but it seems loose while the engine is not running.

I am a decent mechanic, but the MB is not familiar. I found a bolt "thing" that would appear to tighten the belt, but it is maxed out (totally unscrewed).

I have also replaced that shock-absorber thing referred to as the belt tensioner. Further underscoring my ignorance, I don't see how it tensions *anything*.

Questions:
Is there a lock bolt that I am not seeing? Could the belt be stretched but show no visible wear?
There is a ruler-looking gradation just below the water pump. What is that?

Thanks, in advance.

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-Steve

[Benzmac]

There is a hidden bolt. It is located below the water pump and is usually a 19mm head.
The shock does not tension, but dampen the tensioner.
The graduation is for proper tension.
If the belt is loose, the tensioner is bad.
Have it replaced. If you want to do it yourself, it will take a while.

We sell them in the partsshop.

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Benzmac:
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

Can you tell me proper tensioning procedure? What do I do with that 19MM bolt? Just loosen it and adjust the tension with the brass-looking aadjustment bolt?


Thanks.

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-Steve

[Benzmac]

You got it, but if the belt is loose the tensioner is broken. It is like pulling a rubber band; once broken you replace it.

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Benzmac:
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

I tried to loosen that bolt... It is extremely tight. I put all I had into it on a half-inch drive. Is there something I'm missing?

Before I put an extension handle on it and wring something off, I wanted to ask this.

Also, you say it is a long operation to replace the tensioner? What has to come off to do this, and can you tell me the part number and the price at the parts shop?

1987 260E w/2.6L engine.

The belt is not *completely* loose, but it does chirp at full-over turns when maxing out the power steering.

Thanks again.

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-Steve

Steve,
You really should get a manual, theres a lot of stuff that the tensioner is buried under and trying to tell someone in this forum would almost be impossible, the book will give you pictures, torque specs etc. I know the M.B. manual would be hard to get a hold of, but maybe the Haynes book?
If you can't find it, I would be happy to copy the procedure out of my 86 300E manual for you. The parts shop here may even have the CD by now? A purchase that you will use many times over.
See Ya, Chris